Polycycloolefins can be prepared by solution ring opening polymerization of at least one cycloolefin that contains at least one norbornene group. The polymerization reaction yields a honey-like cement containing about 15% solids that comprises polymer solids dissolved in a solvent. The polymer is then precipitated and separated from the cement in a known manner.
The resulting polymer, that can be a homopolymer, copolymer, terpolymer, etc., is brittle and requires modification to make it suitable for commercial applications. For instance, notched Izod value of unmodified polymethyltetracyclodecedene was 44 J/M, which reflects the brittle character of the polymer which for many applications is an unacceptably low impact strength.
It is well known to use rubbery materials as impact modifiers in polymer systems. An attempt was initially made to use a conventional impact modifier for polycycloolefins, however, it proved dissappointing. Only a slight improvement in toughness to 85 J/M was observed when 5 parts of a hydrogenated block copolymer of styrene-butadiene-styrene was dissolved in 5-methyltetracyclododecene and polymerized in bulk in the usual manner with a ring opening catalyst. Other conventional impact modifiers that were also tried were acrylonitrile-butadiene-styrene and methyl methacrylate-styrene-butadiene rubbery materials. These impact modifiers in polymethyltetracyclododecene resulted in negligible improvement in toughness to about 50 J/M.
The use of crystalline polyolefin plastics as impact modifiers, such as polyethylene, pursuant to the invention disclosed herein, is totally unexpected. Although crystalline polyolefin plastics have been used as lubricants in the past, this fact cannot be presumed to suggest their use as impact modifiers in polycycloolefins or any other polymer system. Furthermore, due to their non-rubbery nature, their use as impact modifiers is totally unexpected.
Crystalline polyolefin plastics, especially polyethylene, have been used in the past as lubricants in polyvinyl chloride and other systems. In polymer systems, lubricants or slip agents prevent sticking of the polymer mass to the mill during milling, help to keep the polymer mass from breaking up, and generally facilitate formation of a smooth band on the mill. Amount of polyethylene lubricant used in polymer systems is very small, on the order of a fraction of one part per 100 parts of the polymer on weight basis. If more than about 1 part of polyethylene lubricant is used, it becomes increasingly difficult to disperse. To demonstrate more specifically the amount of polyethylene used as a lubricant, it is pointed out that in polyvinyl chloride, and in chlorinated polyvinyl chloride, only about 0.1 to 0.2 parts thereof is generally used, with a maximum of about 1 part.